Flashback blood collection needle

ABSTRACT

A needle assembly includes a transparent or translucent housing with a fluid inlet end, a fluid outlet end, a flashback chamber, and a venting mechanism therebetween. Substantially axially aligned inlet and outlet cannulas extend from the housing and communicate with the chamber. A sealable sleeve covers the external end of the outlet cannula. Relative volumes of the cannulas, the chamber, and the sleeve are selected to provide rapid reliable flashback indicative of venous entry with an internal vent positioned within the housing so as to divide the interior into first and second chambers, with the second chamber being adapted to maintain a negative pressure therein relative to the external environment so as to inhibit leakage of blood from the needle on withdrawal from the patient.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/824,818 entitled “Flashback Blood Collection Needle” filed Jun. 28,2010, which is a divisional of U.S. patent application Ser. No.12/044,354 entitled “Flashback Blood Collection Needle” filed Mar. 7,2008, the contents of both of which are hereby incorporated by referencein their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device for collecting blood samplesby performing venipuncture on a patient. More particularly, the presentinvention relates to a needle assembly for multiple sample bloodcollection that allows a phlebotomist to determine whether vein entryhas occurred when collecting a blood sample from a patient into anevacuated blood collection tube.

2. Description of Related Art

Venipuncture is the primary method used for acquiring blood samples forlaboratory testing. In performing venipuncture procedures, aphlebotomist must follow several steps simultaneously. Such stepsinclude assessing the patient's overall physical and psychologicalcondition so as to properly select a venipuncture site and technique.The phlebotomist must also select the proper corresponding equipment,perform the technique so as to control bleeding, and properly collectand identify fluid specimens for testing. The phlebotomist mustascertain all of these coinciding factors, as such factors may adverselyaffect the distension of the vein and the length of the venipunctureprocedure.

Various venipuncture devices have been developed to address theabove-described problems. These devices include products intended toassist the phlebotomist in confirming that vein entry has been made, seee.g., U.S. Pat. Nos. 5,222,502 and 5,303,713. Such a device contains aneedle assembly with a housing that defines a chamber therein. A singlecannula pointed at both ends is affixed to the housing. The intravenous(IV) end of the cannula is adapted for penetration of a patient's vein.The non-patient end of the cannula has a sealable sleeve and is adaptedfor penetration of a penetrable stop positioned within an evacuatedcontainer.

Upon vein entry with the intravenous end of the cannula, blood will flowthrough the cannula, into the sealable sleeve and into the housingchamber, which is clear or translucent for visualization (“flashback”).Once air is vented from the flashback chamber, the blood therein ispressurized each time the sealable sleeve is pushed toward the housingchamber upon activation of an evacuated container.

Due to the length of time between vein entry and flashback, thephlebotomist may erroneously believe that satisfactory vein entry hasnot been achieved since there is no immediate indication of vein entryin the see-through chamber. The phlebotomist may therefore unnecessarilyrepeat the venipuncture procedure, requiring replacement of theevacuated container and/or the needle assembly itself. Such a repetitiveprocess prolongs the physical and emotional discomfort endured by thepatient. In such cases, a phlebotomist may use a blood collection set toprovide some entry indication, and will then incur the cost of the bloodcollection set, as well as the cost of a discard tube.

It would therefore be desirable to provide an improved blood collectiondevice that permits blood flow through a relatively short needledirectly into a flashback chamber, thereby providing immediateindication of successful vein entry.

SUMMARY OF THE INVENTION

The invention provides a needle assembly for the extraction of at leastone fluid sample into an evacuated container for laboratory testing. Theneedle assembly provides a clear or translucent housing with sufficientdead space for blood to flow into a flashback chamber for visualizationby the user to confirm successful vein entry, with an internal ventmechanism.

In one embodiment, the invention relates to a needle assembly comprisinga housing defining a housing interior, a cannula having a patientpuncture tip extending from a first end of the housing, and anon-patient puncture tip extending from a second end of the housing. Thenon-patient puncture tip and the patient puncture tip are in fluidcommunication with each other through the cannula, such that the solecommunication path between the housing interior and the externalenvironment is via the patient puncture tip. A porous vent is positionedwithin the housing interior to separate the housing interior into afirst chamber and a second chamber, with the cannula being in fluidcommunication with the first chamber. The porous vent includes pores forpassage of blood therethrough from the first chamber to the secondchamber. The first chamber and the second chamber are configured suchthat upon insertion of the patient needle tip into a patient, bloodflows through the cannula and into the first chamber without sealing theporous vent. Upon application of an evacuated container to thenon-patient puncture tip, blood is drawn from the first chamber and airis drawn from the second chamber, thereby establishing a negativepressure within the second chamber with respect to an externalenvironment of the needle assembly. Blood can thereafter be drawn intothe first chamber and through the porous vent, with a negative pressuremaintained in the second chamber.

In one embodiment, the cannula includes a first end comprising thepatient puncture tip and a second end comprising the non-patientpuncture tip, with an opening between the first end and the second endproviding fluid communication between the cannula and the first chamberof the housing. In an alternate embodiment, the cannula comprises afirst cannula having a patient puncture tip, with the needle assemblyfurther comprising a second cannula including the non-patient puncturetip, with the first cannula and the second cannula substantially axiallyaligned and separated by a gap in fluid communication with the firstchamber of the housing. A sleeve may also extend about the non-patientpuncture tip.

In a particular embodiment, the first end of the housing comprises anelongate longitudinal first portion having a first diameter and thesecond end of the housing comprises a second portion having a seconddiameter larger than the first diameter of the first portion. In such anembodiment, the porous vent may be positioned within the housinginterior between the first portion having a first diameter and thesecond portion having a second diameter. Alternatively, the porous ventmay be positioned within the housing interior at a location spanning thetransition between the first diameter of the first position and thesecond diameter of the second position.

In yet a further embodiment, a method of preventing leakage of bloodfrom a needle assembly is provided. The method involves receiving bloodthrough a patient puncture tip and into a first chamber of a needleassembly, with the needle assembly including a needle housing defining ahousing interior; a cannula having the patient puncture tip extendingfrom a first end of the needle housing; a non-patient puncture tipextending from a second end of the needle housing, the non-patientpuncture tip and the patient puncture tip being in fluid communicationwith each other through the cannula; and a porous vent positioned withinthe housing interior and separating the housing interior into a firstchamber and a second chamber. The cannula is in fluid communication withthe first chamber such that the sole communication path between thehousing interior and the external environment is via the patientpuncture tip, and the porous vent includes pores for passage of bloodtherethrough from the first chamber into the second chamber. Fluidcommunication is established between the non-patient puncture tip and anevacuated collection container, such that blood contained within thefirst chamber is drawn into the evacuated collection container and airis drawn out of the second chamber through the porous vent. As such, anegative pressure is established within the second chamber relative tothe external environment of the needle assembly, such that blood flowsthrough the cannula into the first chamber and contacts the porous vent.Blood is then drawn through the pores of the porous vent toward thesecond chamber such that after removing the patient puncture tip fromthe vasculature of the patient any blood contained within the cannula isdisplaced away from the patient puncture tip based upon the negativepressure established within the second chamber.

Additionally, a further step may include establishing fluidcommunication between the non-patient puncture tip and a secondevacuated collection container prior to drawing blood through thepatient puncture tip and through the cannula into the second evacuatedcollection container, followed by releasing the fluid communicationbetween the non-patient puncture tip and the second evacuated collectioncontainer.

In yet a further embodiment, the invention is directed to a method ofcollecting a sample of blood from a patient into an evacuated bloodcollection tube using a blood collection assembly having a patientneedle tip and a non-patient needle tip and a housing having a flashbackvisualization chamber. The method involves using a needle assemblycomprising a housing having a porous vent positioned therein to separatean interior of the housing into a first chamber forming the flashbackvisualization chamber and a second chamber, the first chamber and secondchamber being configured such that air is drawn out of the secondchamber through the porous vent and into the evacuated blood collectiontube along with the blood sample, thereby establishing a negativepressure within the second chamber. The negative pressure causes bloodto be drawn into the first chamber and contact the porous vent, suchthat after the patient needle tip is removed from the patient, thenegative pressure within the second chamber draws blood from the patientneedle tip toward the second chamber, thereby preventing leakage ofblood from the patient needle tip.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a typical embodiment of the needleassembly of the present invention.

FIG. 2 is a cross-sectional view of a second embodiment.

FIG. 3 is a cross-sectional view of a third embodiment.

FIG. 4 is a cross-sectional view of a fourth embodiment.

FIG. 5 is a schematic view of the needle assembly of FIG. 1 prior touse.

FIG. 6 is a schematic view similar to FIG. 5, but showing the first signof venous entry.

FIG. 7 is a schematic view of a fifth embodiment.

FIG. 8 is a perspective view of a needle assembly having a flash chamberin a further embodiment.

FIG. 9 is a rear perspective view of the needle assembly having a flashchamber of FIG. 8.

FIG. 10 is an exploded view of the needle assembly having a flashchamber of FIG. 8.

FIG. 11A is a cross-sectional view of the needle assembly having a flashchamber of FIG. 8.

FIG. 11B is an enlarged cross-sectional view of a portion of the needleassembly of FIG. 11A.

FIG. 12A is a cross-sectional view of a needle assembly having a flashchamber used in connection with a blood collection assembly in yet afurther embodiment.

FIG. 12B is an enlarged sectional view of a portion of the needleassembly of FIG. 12A.

DETAILED DESCRIPTION

The invention provides a needle assembly for blood collection thatprovides a visual indication of vein entry (“flashback”) upon collectionof a blood or other fluid sample from a patient into one or moreevacuated blood collection tubes and inhibits leakage of the blood orfluid sample from the IV cannula on removal from the patient.

Various embodiments of the present invention are shown in FIGS. 1-7.With reference to FIG. 1, this embodiment is directed to a needleassembly 210 with a housing 212 having a fluid inlet end 214, a fluidoutlet end 216 and a frustum-shaped exterior wall 218 extending betweenthe ends. Exterior wall 218 defines the housing interior 220. Housing212 further includes a cylindrical interior wall 224 that extends in thehousing interior 220 from fluid inlet end 214 substantiallyconcentrically with cylindrical exterior wall 218 to a vent plug 900.Cylindrical interior wall 224 and vent plug 900 define a flashbackchamber 226.

Needle assembly 210 also includes a fluid inlet cannula 236 having anexterior end that defines a sharpened bevel and an interior end 244 thatis mounted fixedly in fluid inlet end 214 of housing 212. Fluid inletcannula 236 is characterized further by a substantially cylindricallumen extending between the ends and communicating with the interior ofhousing 212.

Needle assembly 210 further includes a fluid outlet cannula 252. Outletcannula 252 includes a blunt interior end 254, an exterior end defininga sharpened bevel and a substantially cylindrical lumen extendingbetween the ends. Portions of outlet cannula 252 between the ends aresecurely affixed in outlet end 216 of housing 212. Outlet cannula 252 ismounted so that interior end 254 passes substantially coaxially intointerior wall 224 and so that interior end 254 of outlet cannula 252substantially aligns axially with interior end 244 of inlet cannula 236.Additionally, interior end 254 of outlet cannula 252 is spaced only asmall distance from interior end 244 of inlet cannula 236. An axial gapbetween interior end 254 of outlet cannula 252 and interior end 244 ofinlet cannula 236 that is less than 0.5 mm may result in a flashbackthat is inconsistent.

Cylindrical interior wall 224 is dimensioned relative to outlet cannula252 to achieve both desirable flow of blood through assembly 210 and toachieve effective flashback indication. In particular, cylindricalinterior wall 224 preferably is dimensioned to provide a radial gaparound outlet cannula 252 of about 0.2 mm, as indicated by dimension “c”in FIG. 1. This gap achieves a substantially laminar blood flow withinflashback chamber 226 and prevents blood hemolysis. Additionally, thesmall radial gap between cylindrical inner wall 224 and outlet cannula252 enables a drop of blood to be spread thinly across the radial gap inflashback chamber 226 to provide a magnified flashback indication with avery small volume of blood. Thus, an easily visualized flashbackindication is achieved quickly at the first appearance of blood frominterior end 244 of inlet cannula 236.

Needle assembly 210 further includes a sealable sleeve 261 mounted tofluid outlet end 216 of housing 212 and covering exterior end 258 ofoutlet cannula 252 when sealable sleeve 261 is in an unbiased condition.However, sealable sleeve 261 can be collapsed in response to pressureexerted by the stopper of an evacuated tube for urging exterior end 260of outlet cannula 252 through both sealable sleeve 261 and stopper of anevacuated tube, as known in the art.

The above embodiment is described in terms of a vent plug. However, anyvent mechanism is suitable. The vent mechanism may be, for example, aporous vent plug formed from a matrix or carrier material, typicallyhydrophobic, that is coated with, impregnated with, or otherwisecontains a hydrophilic material that swells on contact with aqueous orwater containing substances. The hydrophobic carrier material can be,but is not limited to, high-density polyethylene,polytetrafluoroethylene, ultra-high molecular weight polyethylene, Nylon6, polypropylene, polyvinylidine fluoride and polyethersulfone. Theswellable nature of the hydrophilic material thereby provides thesealing function in the vent upon contact with blood. It is alsopossible to use a porous vent plug that becomes sealed upon contact withblood using biological phenomena, e.g., by clotting and/or cellagglutination that blocks the vent; a superabsorbant material to sealthe vent by swelling on contact with an aqueous fluid; or a one-wayvalve, (e.g., a thin flap such as plastic film covering a vent, adeformable seal such as a rubber or plastic duckbill valve, or adeformable wrap over a vent). It should be noted that any combination ofthese various mechanisms is also possible.

FIGS. 2-4 show embodiments with varying vent plugs. FIG. 2 shows a ventplug 900 a, which is located at the end of the cylindrical inner wall224 a and fitted into a recess 301 in the housing interior non-patientwall 300. FIG. 3 shows a vent plug in a similar location to that of FIG.2, however, vent plug 900 b has a shoulder 901 b. FIG. 4 shows a ventplug 900 c that is located both within the cylindrical inner wall 224 cand the recess 301 in the housing interior non-patient wall 300, and hasa shoulder 901 c. The vent plug location in each of these embodiments issuch that no air can flow out of the flashback chamber 226 into thehousing interior 220 without passing through the vent mechanism (900 a,b, c).

FIGS. 5 and 6 provide schematic representations of the needle assembly210 of FIG. 1 before and after a conventional venipuncture, in which,the needle assembly 210 is connected to a holder (not shown) andpunctures the patient's skin to make a vein entry. Upon vein entry,blood enters the IV cannula 236 and flows toward the flashback chamber226. The blood flows from inlet cannula 236 into the space between inletand outlet cannula, such that blood flows both into the outlet cannula252 and into flashback chamber 226. At this point in time, flashbackchamber 226 indicates successful vein entry and reduces the volume ofair present in housing 212 shown in FIG. 6. Air that was at atmosphericpressure within the lumen of the IV cannula 248, flashback chamber 226,housing interior 220, and the lumen of the non-patient cannula 262 priorto vein entry, thus experiences compression due to the influence ofvenous pressure and this air is therefore forced through the IV cannula236 shown in FIG. 6 into the flashback chamber 226 and through the ventplug into chamber 220. Blood flow into housing interior 220 is preventedby the vent plug 900, which allows the pressurized air to flow throughit, but seals on contact with blood, thereby trapping the compressed air(at venous pressure) in housing interior 220. Blood flow in the entireneedle assembly ceases once the pressure within chamber 226 and thevenous pressure are equal.

Once the steps set forth in the previous paragraph occur, and venousentry is visually confirmed by the phlebotomist, an evacuated container(not shown), is then inserted into the holder such that exterior end 260of second cannula 252 penetrates the stopper of the container, as knownin the art. Upon penetration of the stopper by second cannula 252, anegative pressure gradient is transmitted to chamber 226, causing bloodto flow from chamber 226 into the container.

The needle assemblies described above desirably should be small forconvenient use, but should be constructed to ensure reliable and rapidflashback. The occurrence of flashback in the needle assembliesdescribed and illustrated above operate pursuant to the ideal gas law.In particular, at very low densities all gases and vapors approach idealgas behavior and closely follow the Boyle's and Charles' laws given by:P ₁ V ₁ =P ₂ V ₂where:

-   -   P₁ denotes the pressure of air within the needle assembly before        needle insertion;    -   P₂ denotes the pressure of air within the needle assembly after        vein entry;    -   V₁ denotes the volume of air within the needle assembly before        vein entry; and    -   V₂ denotes the volume of air within the needle assembly after        vein entry.

Design parameters should keep the needle device as small as possible foreasy use, while ensuring an appropriate volume as specified by thepreceding equation. FIGS. 5 and 6 provide schematic representations ofthe needle assembly 210 of FIG. 1 for purposes of depicting theapplication of the ideal gas law. In this regard, A identifies thevolume of lumen 248 through inlet cannula 236. B denotes the totalvolume of the housing interior 220, flashback chamber 226, lumen 242through outlet cannula 252 and sealable sleeve 261. Referring again tothe preceding equation, P₁ is the pressure within needle assembly 210before use, and hence substantially equals atmospheric pressure.Atmospheric pressure will vary slightly from time to time and fromlocation to location. However, for purposes of this analysis,atmospheric pressure P₁ will be assumed to be 760 mm Hg. P₂ in thepreceding equation is the volume of the dead space in needle assembly210 after vein entry. More particularly, after vein entry, blood willfill lumen 248 of inlet cannula 236, thereby reducing the volume to beoccupied by gas in remaining portions of needle assembly 210 and henceincreasing the pressure of air in the remaining portion of needleassembly 210. A needle assembly with dimensions approximately as shownin FIG. 1 will have a pressure P₂ of about 790 mm Hg at venous pressure(with tourniquet). V₁ in the preceding equation defines the volume ofthe total dead space in needle assembly 210 before use, and hence willequal A+B as shown in FIG. 5. V₂ defines the dead space in the deviceafter vein entry, and with lumen 248 of inlet cannula 236 filled withblood. Hence, V₂ in the preceding equation will equal B. These inputparameters can be employed to define a minimum desired size for therespective components of needle assembly 200 as shown in the followingapplication of the ideal gas law equation.P ₁ V ₁ =P ₂ V ₂P ₁ /P ₂ =V ₂ /V ₁760/790=B/(A+B)0.962=B/(A+B)0.962(A+B)=B0.038B=0.962AB=25.3A

Therefore, dead space in housing 212, outlet cannula 252 and sleeve 261advantageously is at least 25.3 times the volume defined by lumen 248through inlet cannula 236, and most advantageously is about 26 times thevolume of lumen 248. However, other configurations are possible and willfunction as described herein.

The immediate response when an evacuated tube is placed in communicationwith outlet cannula 252 is to draw blood from the vein into tube (notshown). The highest-pressure gradient is always maintained between thevein and the evacuated tube. An axially aligned inlet cannula 236 andoutlet cannula 252, therefore provide an unobstructed path for bloodflow from the vein into evacuated tube.

When the requisite tubes are filled with blood, the needle assembly isremoved from the vein. The sealed nature of the vent plug 900 inhibitsthe pressurized air within housing interior 220 from then moving intothe flashback chamber 226 and into the inlet cannula 236, which couldpromote dripping of blood from the IV cannula tip.

The preceding embodiments show structurally separate inlet and outletcannulas that are axially aligned with one other and placed in closeend-to-end relationship with one another. However, the principals of theinvention described above also can be achieved with a single cannulaformed with a transverse slot or aperture within the flashback chamber.For example, FIG. 7 schematically shows a needle assembly 310 with ahousing 312 that is substantially identical to housing 212 described andillustrated above. Needle assembly 310 differs from needle assembly 210in that a single double end needle cannula 336 is provided and passesentirely through housing 312. More particularly, needle cannula 336includes a venous entry end 338, a non-patient end 340 and a lumen 342extending therebetween. Portions of cannula 336 within inner wall 324include a slot or aperture 344 to provide communication between lumen342 and flashback chamber 336 within inner wall 324. Needle assembly 310functions substantially in the same manner as needle assembly 210described and illustrated above.

FIGS. 8-11 depict a needle assembly in yet a further embodiment of theinvention. In certain embodiments of the needle assembly described withrespect to FIGS. 1-7, the housing interior includes a vent plug 900,which seals the flashback chamber 226/326 from the housing interior220/320. In such previously described embodiments, the vent plug isdescribed as sealing upon flow of blood into the flashback chamber,thereby inhibiting any pressurized air that may build up within thehousing chamber 220/320 (such as upon displacement of air from theflashback chamber 226/326 into the housing chamber 220/320 during theinitial flash procedure) from moving in a reverse direction toward theinlet cannula. In the embodiment of FIGS. 8-11, a porous vent ispositioned within the housing at a location such that the vent dividesthe housing into two chambers having sizes and dimensions to establishpredetermined volumes thereto. Moreover, the porous vent remains porousto blood and does not seal upon contact with blood. Desirably the blooddoes not contact the porous vent at the initial flash indication, butsuch contact occurs at a later point during use of the assembly, as willbe described in more detail herein.

For example, FIGS. 8-11 show a needle assembly 410 similar to thatdescribed in connection with FIGS. 1-6 above. As shown in FIGS. 8-11,needle assembly 410 includes a housing 412 having a fluid inlet end orfirst end 414 and a fluid outlet end or second end 416. Needle assembly410 includes exterior wall 418 defining the housing interior. Exteriorwall 418 extends generally longitudinally at the first end 414 formingan elongate longitudinal first portion 419 having a first diameter. Atsecond end 416, exterior wall 418 forms a second portion 421 that has asecond diameter that is generally larger than the first diameter of thefirst portion 419. Accordingly, housing 412 may form a structure havinga generally T-shaped cross-section. The exterior wall 418 at second end416 may be a separate element 428 that is attachable to main bodyportion 430 forming housing 412, thereby assisting in manufacture andassembly of needle assembly 410. First portion 419 and second portion421 may be arranged relative to each other in a variety of arrangements,so long as they are capable of functioning for transport of airtherebetween as discussed herein.

Needle assembly 410 further includes a fluid inlet cannula 436 extendingfrom first end 414 of housing 412. Fluid inlet cannula 436 includes anexterior end 439 that defines a sharpened bevel at patient puncture tip438, and extends within first end 414 of housing 412, and may be fixedlymounted therein. Fluid inlet cannula 436 is characterized further by asubstantially cylindrical lumen extending between the ends andcommunicating with the interior of housing 412.

Needle assembly 410 also includes a non-patient puncture tip extendingfrom second end 414 of housing 412. As seen in FIG. 10, this may beaccomplished by providing needle assembly 410 with a second cannula inthe form of fluid outlet cannula 452. In particular, the end of fluidoutlet cannula 452 may define a sharpened bevel forming non-patientpuncture tip 462. Fluid outlet cannula 452 extends within second end 416of housing 412, and may be fixedly mounted therein. Fluid outlet cannula452 is characterized further by a substantially cylindrical lumencommunicating with the interior of housing 412. Outlet cannula 452 ismounted within housing 412 so that an interior end 464 passessubstantially coaxially therein such that outlet cannula 452substantially aligns axially with the interior end of inlet cannula 436.Desirably, this is achieved by mounting outlet cannula 452 at a locationadjacent second end 416 of housing 412, such that the interior end 464of outlet cannula 452 extends within housing 412 to a location adjacentthe interior end 439 of inlet cannula 436. As seen in FIG. 11B, theinterior end 464 of outlet cannula 452 is spaced only a small distancefrom the interior end 439 of inlet cannula 436, thereby forming an axialgap therebetween for flow of blood into flashback chamber 426 aboutoutlet cannula 452. The distance between the interior end 464 of outletcannula 452 and the interior end 439 of inlet cannula 436 forming theaxial gap is sufficient to provide for flow of blood into flashbackchamber 426 based upon the patient's blood pressure after venipuncture.In certain embodiments, an axial gap that is less than 0.5 mm may resultin a flashback that is inconsistent.

As seen in FIG. 11B, fluid inlet cannula 436 and fluid outlet cannula452 are positioned and dimensioned within housing 412 so as to achieveboth desirable flow of blood through assembly 410 and to achieveeffective flashback indication. In particular, wall 418 of housing 412is dimensioned to provide a radial gap around outlet cannula 452 ofabout 0.2 mm at an area surrounding the internal end 464 thereof. Thisgap achieves a substantially laminar blood flow within flashback chamber426 and prevents blood hemolysis. Additionally, the small radial gapbetween the inner surface of wall 418 and outlet cannula 452 at the areasurrounding the internal end 464 enables a drop of blood to be spreadthinly across the radial gap in flashback chamber 426 to provide amagnified flashback indication with a very small volume of blood. Thus,an easily visualized flashback indication is achieved quickly at thefirst appearance of blood within flashback chamber 426. It iscontemplated that internal end 464 of outlet cannula 452 may bepartially supported within housing 412, so long as blood flow intoflashback chamber 426 is achieved about the internal end 464.

In an alternate arrangement, a single cannula is provided, similar tothat embodiment discussed in connection with FIG. 7. Such an arrangementis depicted in the embodiment of FIGS. 12A and 12B (shown in connectionwith a blood collection assembly as will be described in more detailherein). In such an arrangement, the fluid inlet cannula and the fluidoutlet cannula represent one single cannula 470, having a patientpuncture tip 438, a non-patient puncture tip 462, and a lumen 442extending therethrough, and with the body of the cannula 470 beingfixedly attached to a portion of the housing 412 and passing entirelythrough housing 412. A portion of cannula 470 extending through housing412 includes one or more openings such as a slot or aperture 444 toprovide communication between lumen 442 and flashback chamber 436 withinhousing 412. In the embodiment seen in FIGS. 12A and 12B, two separateapertures are shown on opposing sides of cannula 470, although it iscontemplated that any number of such openings can be included to providefor blood flow into flashback chamber 436.

Returning to the embodiment of FIGS. 8-11, needle assembly 410 furtherincludes a sealable sleeve 461 mounted to fluid outlet end 416 ofhousing 412. This may be accomplished by providing a mounting protrusion429 at second end 416 of housing 412, such as on element 428, withsealable sleeve 461 representing an elastomeric element that can befrictionally fit or otherwise affixed over protrusion 429. Sealablesleeve 461 covers non-patient puncture tip 462 at the exterior end ofoutlet cannula 452 when sealable sleeve 461 is in an unbiased condition.However, sealable sleeve 461 can be collapsed in response to pressureexerted by the stopper of an evacuated tube for urging exterior end 460of outlet cannula 452 through both sealable sleeve 461 and the stopperof an evacuated tube, as known in the art.

The embodiment of FIGS. 8-11 further includes a porous vent 910positioned within the interior of housing 412. Porous vent 910 ispositioned within housing 412 to divide housing 412 into two distinctchambers, namely, a first chamber represented by flashback chamber 426and a second chamber represented by secondary chamber 427. Porous vent910 may be constructed of a suitable material as described above withrespect to vent plug 900, albeit without the hydrophilic material thatswells on contact. In this manner, porous vent 910 is adapted to ventair therethrough, and represents a porous structure including aplurality of pores that allow for passage of blood therethrough. Asdiscussed in more detail herein, during use of needle assembly 410, theinternal pores within porous vent 910 at least partially fill with blooddue to the negative pressure established within secondary chamber 427.Such filled pores in combination with the negative pressure withinsecondary chamber 427 prevent air flow between the secondary chamber 427and the flashback chamber 426, and provide for fluid resistance of theblood flow through porous vent 910, as will be described in furtherdetail.

Desirably, porous vent 910 is positioned within the interior of housing412 between first portion 419 and second portion 421. In this manner,first portion 419 of housing 412 essentially defines the flashbackchamber 426, and second portion 421 of housing 412 essentially definesthe secondary chamber 427. Alternatively, porous vent 910 may bepositioned within the interior of housing 412 at a location spanning thetransition between the first diameter of first portion 419 and thesecond diameter of second portion 421, as shown in the embodiment ofFIGS. 12A and 12B. In any event, porous vent 910 is generally acylindrically-shaped member with a central opening therein axiallyencircling a portion of the cannula, particularly fluid outlet cannula452.

The interior volume of housing 412 is defined by the sum of the volumesof flashback chamber 426 and secondary chamber 427 as well as the volumerepresented by the pores of porous vent 910. Such interior volume isconfigured so as to provide for certain attributes to the needleassembly 410, in particular with respect to the ability of the secondarychamber 427 to be at least partially evacuated of a portion of the airtherein to establish a negative pressure therein upon application of anevacuated tube to needle assembly 410 during use thereof. Such negativepressure within secondary chamber 427 draws blood through the pores ofporous vent 910 based on when blood contacts porous vent 910 andpartially fills the pores thereof. In a particular embodiment of theinvention, the overall interior volume of housing 412 may be from about300 mm³ to about 400 mm³. Such a volume is particularly useful for theintended use of needle assembly 410 for conventional venipuncture fordrawing a blood sample from a patient using a needle cannula having aconventional gauge for venipuncture as is known in the art. With such aninternal volume, porous vent 910 is desirably positioned within housinginterior so as to define flashback chamber 426 as having a volume thatrepresents from about 5 percent to about 20 percent of the total overallvolume of housing 412, desirably from about 7 percent to about 12percent of the total overall volume of housing 412, including the volumeof secondary chamber 427 and the volume of the pores within porous vent910. Such a ratio of the flashback chamber 426 to the total overallvolume of the housing 412 assures that flashback chamber 426 hassufficient volume to properly visualize the initial flash, and desirablywhile preventing blood from fully contacting the porous vent 910 atinitial venipuncture, based on the initial build-up of pressure withinsecondary chamber 427 caused by venous pressure forcing the blood intoflashback chamber 426. Such volume ratios are effective for the intendeduse as described in further detail herein, wherein blood flowing intoflashback chamber 426 upon initial venipuncture does not contact porousvent 910, and wherein at least a portion of the air is drawn out fromsecondary chamber 427 based upon application of an evacuated bloodcollection tube to the needle assembly 410. In this manner, secondarychamber 427 can effectively draw blood from within flashback chamber 426and from within fluid inlet cannula 426 toward secondary chamber 427,such as into and through porous vent 910, when patient puncture tip 438is removed from the patient and is exposed to the external environment.In one particular embodiment, the total interior volume of the housing412 is about 380 mm³, with the flashback chamber 426 having a volume ofabout 30 mm³, the secondary chamber 427 having a volume of about 300mm³, and the pores of the porous vent 910 representing a volume of about50 mm³.

Needle assembly 410 may be assembled as follows. Fluid inlet cannula 436is positioned through first end 414 of housing 412 such that the openinterior end 439 is positioned within an interior portion of housing 412at first portion 419 and patient puncture tip 438 extends externally offirst end 414. Fluid outlet cannula 452 is positioned within housing 412through the opposite end, such that open internal end 464 is positionedwithin an interior portion of housing 412 at first portion 419 adjacentinterior end 439 of fluid inlet cannula 436, with a slight gaptherebetween, and with non-patient puncture tip extending externally ofsecond end 416. Fluid inlet cannula 436 and fluid outlet cannula 452 maybe affixed therein in any known manner, desirably through a medicalgrade adhesive.

In alternate embodiments including only a single cannula 470, suchcannula 470 is affixed within housing 412 such that opening 472 ispositioned within the interior of housing 412 at first portion 419, withpatient puncture tip 438 extending externally of first end 414 andnon-patient puncture tip 462 extending externally of second end 416.

Porous vent 910 is then inserted within housing 412 and positioned overfluid outlet cannula 454 (or over the single cannula 470), and element428 is thereafter affixed to the second end 416, enclosing the interiorof housing 412. Sealable sleeve 461 is then affixed over protrusion 429.As such, the interior of housing 412 is closed from the externalenvironment, with the sole path for fluid communication between theinterior of housing 412 and the external environment being providedthrough the patient puncture tip 438.

Needle assembly 410 assembled as such can be used in connection with ablood collection tube holder 800, as depicted in the embodiment shown inFIG. 12. Such assembly may be accomplished through the rear open end ofblood collection tube holder 800, so that the entire needle assembly 410is inserted to a portion where at least patient puncture tip 438 and atleast a portion of inlet cannula 436 extend out through the front end ofblood collection tube holder 800. In embodiments where second portion421 of needle assembly 410 is radially larger than first portion 419,such an insertion and arrangement enables the secondary chamber 427 tobe fully contained within the internal space within collection tubeholder 800, and with flashback chamber 426 extending out from a frontend thereof.

In use, needle assembly 410 may be provided with collection tube holder800 attached thereto. Patient puncture tip 438 is inserted through theskin of a patient and into the patient's vasculature, desirably into avein. Upon venipucture, a closed environment is achieved within housing412, since housing 412 is an entirely closed structure, and sincesealable sleeve 461 closes off the only outlet of housing 412 (i.e.,fluid outlet cannula 452). The patient's blood pressure causes blood toflow through patient puncture tip 438, into fluid inlet cannula 436, andout interior end 439 (or through opening 472 in the embodiment of FIG.12), into flashback chamber 426 surrounding interior end 464 of outletcannula 452. The transparent or translucent nature of housing 412permits visualization of the blood within flashback chamber 426,providing an indication that venipuncture is achieved.

Since the interior of housing 412 is a closed environment, the flow ofblood into flashback chamber 426 causes air to be trapped within thehousing interior, including within flashback chamber 426, porous vent910 and secondary chamber 427, as well as within fluid outlet cannula452, causing such trapped air to be slightly pressurized therein.Flashback chamber 426 and secondary chamber 427 are configured throughtheir size and dimensions such that the volumes thereof permit blood toflow into flashback chamber 426 at this initial venipucture, but thebuild up of air pressure within the pores of porous vent 910 and withinsecondary chamber 427 prevents blood from fully contacting porous vent910, and desirably prevents blood from even partially contacting porousvent 910 at the initial venipuncture.

After such initial venipuncture and flash visualization, a samplecollection container having a negative pressure therein, such as anevacuated blood collection tube (not shown) as is commonly known in theart, is inserted within the tube holder 800. The stopper (not shown) ofsuch evacuated container contacts and displaces sealable sleeve 461,causing non-patient puncture tip 462 to puncture through sealable sleeve461 and through the stopper of the evacuated container. At this point,fluid communication is established between the non-patient puncture tip462 and the interior of the evacuated collection container. The negativepressure within the evacuated collection container draws the blood thathas collected within flashback chamber 426 into fluid outlet cannula 452and into the evacuated collection container. Along with the blood withinflashback chamber 426, the negative pressure within the evacuatedcollection container will also draw at least a portion of the air out ofthe flashback chamber 426 and out of the secondary chamber 427 throughthe pores of porous vent 910, toward and into the evacuated collectioncontainer. In addition, the close proximity and alignment of fluidoutlet cannula 452 and fluid inlet cannula 426 causes blood to be drawnfrom fluid inlet cannula 436 and from the patient, simultaneously withsuch air being drawn from the flashback chamber 426 and secondarychamber 427.

Such drawing of air reduces the pressure within the flashback chamber426 and the secondary chamber 427, establishing a negative pressuretherein with respect to the patient's bloodstream and with respect tothe external environment. This negative pressure that has beenestablished within the interior of housing 412, and specifically withinflashback chamber 426 and secondary chamber 427, draws additional bloodfrom within fluid inlet cannula 436 and from the patient into flashbackchamber 426, with the blood contacting porous vent 910. With such bloodfilling flashback chamber 426, the blood fully contacts the surface ofporous vent 910 that extends within flashback chamber 426, and begins tofill the pores of porous vent 910. Such filling of the pores of porousvent 910 that are directly at the interface of porous vent 910 andflashback chamber 426 closes off the porous vent from airflowtherethrough, but does not fully act as a seal, in that the blood doesnot cause the material of the porous vent to swell or close off to airflow, but instead merely physically fills the voids within the porousvent. Moreover, since a portion of the air within secondary chamber 427has been drawn out from secondary chamber 427, secondary chamber 427represents a closed chamber with a negative pressure therein relative tothe external environment. Secondary chamber 427 will therefore continueto have a drawing effect on the blood within the pores of porous vent910 and within flashback chamber 426 through the pores of porous vent910 toward secondary chamber 427, without releasing any air from thesecondary chamber 427 in the opposite direction due to the pores ofporous vent 910 at the interface of the flashback chamber 426 beingfilled with blood, thereby effectively preventing air flow throughporous vent 910 due to the filled pores. The draw created by thenegative pressure within secondary chamber 427 has a fluid resistancebased on the blood filling the pores of porous vent 910 and based on thetortuous path created by the pores of porous vent 910, and therefore isa gradual draw with reduced fluid movement.

At this point, the evacuated collection container and the secondarychamber 427 are both at a negative pressure with respect to the externalenvironment (and with respect to the patient's bloodstream), andtherefore both effect a draw from the fluid inlet cannula 436. Thismutual drawing effect may essentially establish an equilibrium withinthe flashback chamber 426, such that the blood contained within theflashback chamber 426 is not drawn toward or into either the secondarychamber 427 through the pores of porous vent 910 or into the evacuatedcollection container through the fluid inlet cannula 436, but insteadessentially remains within flashback chamber 426 in a steady state. Thenegative pressure of the evacuated collection container draws blooddirectly from the patient through fluid inlet cannula 436, due to theclose proximity and alignment of fluid outlet cannula 452 and fluidinlet cannula 426, as well as due to the equilibrium established withinflashback chamber 426 (based on the opposite draw forces between theevacuated collection container and the evacuated secondary chamber 427).The continual draw of blood into the evacuated collection containergradually causes the pressure within the collection container toincrease.

Once the evacuated collection container is filled with the desiredamount of blood, the container is removed from the non-patient puncturetip 462, thereby releasing the fluid communication between thenon-patient puncture tip 462 and the evacuated collection container,with sealable sleeve 461 then covering and closing off non-patientpuncture tip 462. Absent such draw from the negative pressure of theevacuated collection tube, the negative pressure within the secondarychamber 427 effects a slight draw on the blood within flashback chamber426 through the pores of porous vent 910. Such draw, however, is slowand gradual, due to the tortuous path of blood flow through the pores ofporous vent 910.

Additional evacuated collection containers can thereafter be insertedinto tube holder 800 and used for sample collection through non-patientpuncture tip 462 as described above, by placing a second evacuatedcollection container within the holder 800 and establishing fluidcommunication between the non-patient puncture tip 462 and the interiorof the evacuated collection container by puncturing the stopper, asdiscussed. In such further sampling, the evacuated collection containerand the secondary chamber 427 are both at a negative pressure, andtherefore both effect a draw from the fluid inlet cannula. As above,this effect essentially establishes an equilibrium within the flashbackchamber 426, thereby preventing the blood contained within the flashbackchamber 426 from being drawn toward or into the secondary chamber 427(through the porous vent 910). The negative pressure of the evacuatedcollection container draws blood directly from the patient through fluidinlet cannula 436 as discussed above, due to the close proximity andalignment of fluid outlet cannula 452 and fluid inlet cannula 426. Onceany such additional evacuated collection containers are filled with thedesired amount of blood, the container is removed from the non-patientpuncture tip 462, thereby releasing the fluid communication between thenon-patient puncture tip 462 and the evacuated collection container,with sealable sleeve 461 then covering and closing off non-patientpuncture tip 462.

Once all of the desired blood samples have been drawn in this manner,patient puncture tip 438 is removed from the vasculature of the patient(i.e., from the bloodstream), thereby exposing the opening of patientpuncture tip 438 to the external environment. Since the solecommunication path between the housing interior and the externalenvironment is through patient puncture tip 438, the negative pressureestablished within secondary chamber 427 relative to the externalenvironment will affect a gradual draw on the blood contained withinflashback chamber 426 and within fluid inlet cannula 436 toward andthrough porous vent 910. Such drawing effect will displace and move anyblood contained within fluid inlet cannula 436 away from patientpuncture tip 438, toward secondary chamber 427, thereby preventing anyblood from leaking from patient puncture tip 438 out of fluid inletcannula 436. Such negative pressure within secondary chamber 427 maycontinue to have a gradual drawing effect through the porous vent 910for a prolonged period of time after removal of patient puncture tip 438from the patient, and may draw all of the remaining blood containedwithin fluid inlet cannula 436 and flashback chamber 426 through porousvent 910 and/or into secondary chamber 427. Needle assembly 410 can thenbe properly disposed of in known manner.

The relative dimensional calculations, volumes and pressures apply toboth illustrated and unillustrated embodiments of the invention.Accordingly, the scope of the as defined by the appending claims is notlimited to the specific illustrated embodiments. Various other changesand modifications may be effected therein by one skilled in the artwithout departing from the scope or spirit of the invention, and it isintended to claim all such changes and modifications as fall within thescope of the invention.

What is claimed is:
 1. A method of preventing leakage of blood from aneedle assembly comprising: a) receiving blood through a patientpuncture tip and into a first chamber of the needle assembly, the needleassembly comprising: i) a needle housing defining a housing interior,said housing comprising the patient puncture tip extending from a firstend of the housing and a non-patient puncture tip extending from asecond end of the housing, and ii) a porous vent positioned within thehousing interior and separating the housing interior into a firstchamber and a second chamber, with the non-patient puncture tip and thepatient puncture tip being in fluid communication with each other withinthe first chamber such that the sole communication path between thehousing interior and the external environment is via the patientpuncture tip, the porous vent including pores for passage of bloodtherethrough from the first chamber into the second chamber; b)establishing fluid communication between the non-patient puncture tipand a negative pressure source such that blood contained within thefirst chamber is drawn out of the non-patient puncture tip and air isdrawn out of the second chamber through the porous vent, therebyestablishing a negative pressure within the second chamber relative tothe external environment of the needle assembly such that blood flowsthrough a cannula into the first chamber and contacts the porous vent;and c) drawing blood through the pores of the porous vent toward thesecond chamber based upon the negative pressure established within thesecond chamber such that blood contained within a lumen of the patientpuncture tip is displaced away from the patient puncture tip and towardthe second chamber.
 2. The method of claim 1, wherein the receiving stepa) comprises receiving blood through the lumen of the patient puncturetip from a patient's bloodstream, and the drawing step c) displacesblood away from the patient puncture tip after removing the patientpuncture tip from the patient's bloodstream.
 3. The method of claim 1,including a further step after step b) and prior to step c) comprisingreleasing the fluid communication between the non-patient puncture tipand the negative pressure source.
 4. The method of claim 3, wherein thenegative pressure source comprises an evacuated collection container andwherein the step of releasing the fluid communication comprises removingthe evacuated collection container from the non-patient puncture tip andsealing the non-patient puncture tip from the external environment. 5.The method of claim 4, wherein the needle assembly comprises a sealablesleeve extending about the non-patient puncture tip, said sealablesleeve being displaceable so as to permit the fluid communicationbetween the evacuated collection container and the non-patient puncturetip in step b), and so as to reseal upon removal of the evacuatedcollection container from the non-patient puncture tip.
 6. The method ofclaim 5, including a further step after said step of releasing the fluidcommunication between the non-patient puncture tip and the evacuatedcollection container, comprising establishing fluid communicationbetween the non-patient puncture tip and a second evacuated collectioncontainer, such that blood is drawn through the lumen of the patientpuncture tip into the second evacuated collection container, followed byreleasing the fluid communication between the non-patient puncture tipand the second evacuated collection container.